1. Technical Field
The present invention relates to a process for recovering oil from an oil-bearing subterranean formation and in particular to a process wherein an aqueous partially hydrolyzed polyacrylamide solution produced under controlled conditions is employed to recover oil from the formation.
2. Background Information
Aqueous solutions of partially hydrolyzed polyacrylamide (PHPA) are commonly used in oil recovery processes. For example, U.S. Pat. Nos. 2,827,964 to Sandiford et al and 3,039,529 to McKennon teach the use of an aqueous PHPA solution as an oil-displacing drive fluid and U.S. Pat. No. 3,467,187 to Gogarty et al teaches its use as a mobility buffer for a micellar displacement fluid.
A number of processes for producing dilute PHPA solutions which may be used in the above-cited oil recovery processes are likewise well known. For example, U.S. Pat. Nos. 3,558,759 to Sarem, 3,370,649 to Wolgemuth and 4,433,727 to Argabright et al teach polymerization processes for manufacturing PHPA solutions. These patents disclose a broad range of values for polymerization parameters wherein the processes are operable. Thus far, however, PHPA manufacturers have had to resort to trial and error when selecting specific values of polymerization reaction parameters to effectively produce dilute PHPA solutions having predetermined properties because the sensitivity of these properties to variations in the polymerization reaction parameters within known operable ranges has not been recognized. Unfortunately, this haphazard approach is unsatisfactory because quality control and reproducibility of the PHPA product are difficult to achieve.